1. Field of the Invention
The present invention relates to a thin film magnetic head having at least an inductive magnetic transducer for recording and, more particularly, to a thin film magnetic head of a perpendicular recording type for magnetizing a recording medium in the direction orthogonal to the surface of the recording medium at the time of recording.
2. Description of the Related Art
In recent years, for example, in the field of development of a magnetic recording medium (hereinbelow, simply called “recording medium”) such as a hard disk, recording density is increasing and a magnetization transition region in a recording medium is being narrowed. It accompanies an unintended magnetization inverting phenomenon caused by thermal fluctuation, that is, recording demagnetization is becoming a problem. In place of the conventional “longitudinal recording method”, the “perpendicular recording method” is being regarded as a promising method which deals with the problem of recording demagnetization. In the perpendicular recording method, different from the longitudinal recording method in which the orientation of a signal magnetic field is set to an in-plane direction (longitudinal direction) of a recording medium, the orientation of a signal magnetic field is set to a direction orthogonal to the surface of a recording medium. A thin film magnetic head of the perpendicular recording method has, as a part for a recording process, a head (single-pole head) disposed perpendicular to a recording medium.
To realize high-density recording higher than about 100 Gbpsi, the perpendicular recording method is employed as the recording method and, in addition, for example, the following items have to be considered.
First, to assure excellent recording capability for a recording medium having a high coercive force, a material having high saturation magnetic flux density has to be used as the material of a single-pole head. An example of the material having high saturation magnetic flux density is an alloy material introduced in “Slater-Pauling curve” by Bozoroth, concretely, an iron cobalt alloy (FeCo; Fe=30 percent by weight) having the highest saturation magnetic flux density (about 2.45 T (tesla)) in bulk alloys. Although an iron cobalt alloy containing 30 to 50 percent by weight of an iron component has an advantage from the viewpoint of saturation magnetic flux density, magnetostriction is large so that it is difficult to obtain a proper soft magnetic characteristic. There is, consequently, a problem that a desired magnetic domain structure is not easily obtained by the material of a single-pole head.
Second, to assure a stable recording characteristic, as a recording medium to be used in combination with the single-pole head, for example, a recording medium of a two-layered configuration having a stacked-layer structure of a soft magnetic layer and a recording magnetic layer has to be used. In the recording medium of the two-layered configuration, a magnetic flux for recording which is emitted from the single-pole head can be efficiently pulled into the soft magnetic layer by using the soft magnetic layer functioning as a flux path. Although the recording medium of the two-layered configuration has an advantage from the viewpoint of efficiency of pulling the magnetic flux for recording, it also has a problem such that when a magnetic flux is leaked from the single-pole head, recording magnetization of the recording medium is disturbed due to the leaked magnetic flux, and information may be unintentionally erased.
Third, to assure stable recording operation, the magnetic domain structure of the single-pole head has to be controlled. Generally, in a magnetic material, a magnetic domain structure is formed so that the sum of (1) magnetic static energy, (2) other magnetic anisotropic energies including shape magnetic anisotropy, and (3) magnetic domain wall energy becomes the minimum as a whole. If control on the magnetic domain structure of the single-pole head is insufficient, a magnetic flux is unintentionally leaked from the single-pole head due to occurrence of a magnetic domain change (shift of the magnetic domain wall) and it is feared that the recording magnetization of the recording medium is disturbed by the leaked magnetic flux.
Among the three items, particularly, the point of controlling the magnetic domain structure of the simple-pole head is largely related to the unintended magnetic flux leak phenomenon, so that it is important. Examples of a known technique for controlling the magnetic domain structure of the single-pole head are a method of alternately stacking a soft magnetic layer and a nonmagnetic layer (refer to, for example, Japanese Patent Publication No. Hei 6-66188 and Japanese Paten Laid-open No. Hei 5-54320) and a method of alternately stacking a magnetic artificial lattice film and a nonmagnetic insulating film (refer to, for example, Japanese Patent No. 2,543,374).
However, when considering trends that the saturation magnetic flux density of the material of a head is increasing and the recording track width is being narrowed in association with rapid increase in recording density of recent years, in spite of importance of controlling the magnetic domain structure of a single-pole head in order to prevent unintended magnetic flux leak, the above-described existing techniques have a problem that it is difficult to sufficiently properly control the magnetic domain structure of the single-pole head. In particular, if it is intended to prevent the unintentional leak of magnetic flux as much as possible, as described above, it is necessary to control the magnetic domain structure of the single-pole head and, in addition, to properly form the shape of the single-pole head.